The following invention relates to a system for measuring the total velocity of a target, and more particularly relates to a passive electro-optical system for measuring two components of the total velocity: one parallel to the system line-of-sight and one perpendicular to the system line-of-sight.
Most speed detection systems require a transmitter to transmit energy towards a moving target that is reflected back to a receiver. Laser ranging systems measure the time of transmission and the return of the energy in order to calculate the range to the target and its speed. Radar ranging systems, such as the radar guns used by law enforcement agencies for traffic control, use the principle of Doppler frequency shift to calculate target speed. One problem with radar as a traffic control device is that target acquisition and measurement are ambiguous. Generally it can not be determined which target out of a multitude of possible targets is responsible for generating any particular speed indication. Another problem is that radar can be detected by receivers tuned to the proper frequency. Yet another problem with Doppler radars is that they cannot measure range. Available laser ranging systems can measure range, but are detectable by receivers (laser detectors), are more expensive than radar systems, and are more difficult to aim than radar systems.
U.S. Pat. No. 5,586,063 to Hardin et al., which is assigned to the assignee of this application and is incorporated herein by reference, is directed to a passive optical speed and distance measuring system (the ""063 system). Specifically the ""063 system includes a pair of camera lenses positioned along a common baseline a predetermined distance apart and controlled by an operator to capture images of a target at different times. The camera lenses are focused on light sensitive pixel arrays that capture target images at offset positions in the line scans of the pixel arrays. A video signal processor with a computer determines the location of the offset positions and calculates the range to the target by solving the trigonometry of the triangle formed by the two camera lenses and the target. Once the range to the target is known at two different times the speed of the target is calculated.
The ""063 system measures only one component of velocity, the component in the direction of its line-of-sight. This component, in the general case, is less than the velocity of a target such as a moving object.
What is needed then is a system that is capable of measuring the total velocity of a target.
The system of the present invention measures the total displacement of a target that is shown graphically as displacement vector xcex4R. The total velocity is then obtained by dividing by the time interval over which the displacement occurred. By comparison, the ""063 system can measure only one component of this velocity (the component along the ""063 system LOS). Further, the system of the present invention is able to resolve the displacement vector into two components; one component XR that is parallel to the system LOS and one component XR that is perpendicular to the system LOS. The corresponding x and y velocity components, VX and VY respectively, are obtained by dividing by the time interval over which the displacement occurred.
Further, the system of the present invention may be used to track an object or to control a sensor platform to keep a system line-of-sight (LOS) pointed at a moving object because this system is capable of deriving the angle between the LOS of the system and the velocity vector of the moving target.
The present invention is directed to a passive electro-optical range and total velocity measuring system having first and second cameras positioned along a common baseline. A first camera control system activates the first camera at a first instance to capture a target image of a target at location T1 and at a second instance to capture a target image of the target at location T2. A second camera control system activates the second camera at the first instance to capture a target image of the target at location T1 and at the second instance to capture a target image of the target at location T2. A range computer calculates ranges from the first camera, the second camera, and a baseline midpoint to a target at location T1 and location T2. An angles computer calculates target displacement. A velocity computer calculates total target velocity, track velocity, and cross-track velocity, where track velocity and cross-track velocity are components of the total velocity.
A separate preferred embodiment of the present invention is directed to a method for measuring the range and total velocity of a target using a passive electro-optical system. Specifically, the method includes the steps of activating first and second image acquisition devices at a first instance to capture a target image of a target at location T1 and at a second instance to capture a target image of the target at location T2. The next steps are calculating steps in which the ranges from said first and second image acquisition devices to said target at locations T1 and T2, the target displacement xcex4R, the total target velocity V, the track velocity VX, and the cross-track velocity VY are calculated.